This invention relates to pneumatic agricultural tires for use on farm tractors and similar agricultural type vehicles. Tractor tires must have good vibration characteristics on and off the road while maintaining good traction or drawbar characteristics. Such tires must also provide for the removal of soil, mud, etc., during in-field use.
These design factors are particularly problematic on tires with wide section widths of 600 mm or greater. These tires are commonly employed in multiples of two or more per drive wheel position and in applications where the tractor has four wheel drive these tires are employed on both front steer and rear axle positions.
A commonly employed tire is the Goodyear DT 820 Super Traction Radial. This tire has excellent drawbar characteristics particularly in difficult heavy moist soil. The tire 10 as depicted in FIG. 1 has two sets of long 41,42 lugs oriented at about 45.degree.. The long lugs 41,42 extend from each tread 11 edge to the center of the tread and have a depth 25% deeper than conventional R-1 tractor tires. This tire 10 was used as a control tire for comparative purposes.
As can be observed from the figure this prior art tire's long lugs 41,42 and wide spacing of the lugs although excellent for traction can be somewhat difficult in turning maneuvers. The large lugs 41,42 tend to act like a gear meshing in the soil and as the vehicle attempts to turn the tires 10 must decouple from the soil. This gear like effect is particularly troublesome in the steer axle position.
A second problem created by this deep long bar lug is soil compaction. Soil compaction is considered a serious problem which can result in increased topsoil erosion. The tractor tire lugs compress the soil. The compressed soil is less capable of absorbing rainfall which contributes to runoff of water, which in turn leads to soil erosion. The loss of topsoil means that the productive agricultural farmland becomes less productive requiring an increase in fertilizer and chemical usage to compensate for the depleted soil.
In 1992, The Goodyear Tire & Rubber Company introduced a new tractor tire having two sets of primary and secondary lugs. The tire is commercially sold as the DT 710 and is described in U.S. Pat. No. 5,046,541. As described in the patent, this tire has good traction, vibration and cleaning characteristics. These primary and secondary lugs are shorter in length than most tractor tire lugs. The tire effectively increases the number of lugs, and, therefore, has an increase in lug surface area. This increases the performance capabilities of the tire. The flexible nature of these relative short primary and secondary lugs may also help reduce the soil compaction potential of the tire even though more lug surface area is employed.
As the DT 710 product line was being developed and released into production the inventors observed there was a problem implementing this design into the large wide base tire sizes have 600/65 cross sections and larger.
Several attempts were made to scale the DT 710 tread layout on these larger sizes but the between-lug void in the shoulder area of the tread was too large and considered unacceptable. There was concern that the overall durability of the design would be compromised due to a reduction in lug and center element surface area as compared to conventional single lug patterns in the wide base tire sizes. In addition, the large shoulder void would most likely deter rather than enhance the ride and handling performance requirements. This was a very important point to consider because lug-induced vibration requirements must continue to improve in order to meet customer expectations.
When it became apparent to the inventors that the scaling limitations as described could not be corrected using the DT 710 tread pattern, a decision was made to develop a new version of the lug/center element concept. Many candidates were considered and one tread pattern in particular seemed quite promising.
That tread configuration is the subject of the present invention. A tread pattern made according to the present invention can exceed the excellent traction and vibration performance of the prior art tires while reducing soil compaction.